This invention relates to a method of controlling the operating amount of an operation control means for an internal combustion engine, and more particularly to a method of this kind which is adapted to constantly properly correct differences between the actual values of opening areas of the throttle valve and control valves for controlling the quantity of supplementary air being supplied to the engine, and the detected values of the opening areas of the same valves, to thereby control with accuracy the operating amount of the operation control means to a required value while the engine is operating in a low load condition such as at idle.
A method has been proposed, e.g. by Japanese Provisional Patent Publications (Kokai) Nos. 58-88436 and 53-8434, which determines a basic operating amount of operation control means for controlling the operation of the engine, such as a basic fuel injection amount to be supplied to the engine by a fuel supply quantity control system, a basic value of spark ignition timing to be controlled by an ignition timing control system, and a basic recirculation amount of exhaust gases to be controlled by an exhaust gas recirculation control system, in dependence on absolute pressure in the intake pipe of the engine and engine rotational speed, and corrects the basic operating amount thus determined in response to the temperature of intake air, the temperature of engine cooling water, etc., to thereby set a desired operating amount for the operation control means with accuracy. With this proposed method of determining operating amounts of the operation control means in dependence on the intake pipe absolute pressure and the engine speed (generally called "the speed density method", and hereinafter merely referred to as "the SD method"), while the engine is operating in a low load condition, i.e. in an idling condition, there occurs a reduction in a rate of change in the intake pipe absolute pressure relative to the lapse of time with respect to a rate of change in the engine speed relative to the lapse of time and also pulsation occurs in the intake pipe absolute pressure, making it difficult to set with accuracy an operating amount such as a fuel supply quantity in accordance with operating conditions of the engine, resulting in hunting of the engine rotation.
To solve the above problem, a method has been proposed, e.g. by Japanese Patent Publication No. 52-6414, which is based upon the recognition that the ratio (PBA/PA') of intake pipe pressure PBA downstream of the throttle valve to intake pipe pressure PA' upstream of the same valve is below a critical pressure ratio (=0.528) at which the intake air forms a sonic flow, while the engine is operating in a low load condition such as at idle, and that the quantity of intake air passing the throttle valve is not dependent upon pressure PBA in the intake pipe downstream of the throttle valve or pressure of the exhaust gases but on the valve opening of the throttle valve. Therefore, this proposed method detects the valve opening of the throttle valve alone to thereby detect the quantity of intake air while the engine is operating in the low load condition, and then sets an operating amount such as a fuel injection quantity on the basis of the detected value of the intake air quantity.
If the manner of detecting the intake air quantity, described above, is applied to control of the fuel injection quantity for instance, it is necessary to determine a fuel injection quantity as a function of the engine speed as well as the intake air quantity determined as above. This is because, although the quantity of intake air passing the throttle valve per unit time is constant so far as the opening area of the throttle valve remains the same, the quantity of air sucked into the engine per suction stroke varies in dependence on the engine speed. Thus, a basic fuel injection period Ti of the fuel injection valves is determined by using the following equation, for supply of fuel to the engine: EQU Ti=(K.theta.+KAIC+ . . . ).times.Me
where K.theta., KAIC, etc. represent opening area coefficients which are determined by respective opening areas of the throttle valve, control valves which control the quantity of supplementary air being supplied to the engine, etc. Me represents the interval of time between adjacent pulses of a pulse signal having its pulses generated at predetermined crank angles of the engine, e.g. at the top-dead-center (TDC) positions of pistons of the engine, a value of which is proportional to the reciprocal of the engine speed.
With this method of determining the basic fuel injection period by the use of the equation given above (hereinafter merely called "the KMe method"), it can occur that the opening area coefficients K.theta., KAIC, etc. are not set to accurate values corresponding to the actual opening areas, due to differences in value between the actual opening areas of the throttle valve and the control valves and the detected opening areas of the same valves, as caused by variations in the performance or locating error at installation of the throttle valve opening sensor, or by adhesion of carbon etc. contained in the blow-by gas and the atmosphere to the throttle valves and the control valves. Further, in the event of clogging of the air filter attached to an end of the intake pipe opening into the atmosphere, even if the actual opening areas of the throttle valve and the control valves are detected with accuracy, the actual intake air quantity can be smaller than a value of intake air quantity detected from the actual opening areas, resulting in the air/fuel mixture being enriched. To avoid these disadvantages, a possible measure may be to add or subtract a certain correction value which is a fixed value to or from the basic fuel injection period Ti value determined by the aforegiven equation at delivery of engines from the factory or at maintenance of same. According to this measure, however, since the basic fuel injection period Ti is calculated by multiplying the sum of the values of the opening area coefficients K.theta., KAIC, etc. by the value of time interval Me between adjacent TDC pulses, proportional to the reciprocal of the engine speed, accurate correction of the basic fuel injection period Ti cannot be achieved by the use of the certain correction value at engine rotational speeds other than a reference engine speed with reference to which the certain correction value has been set.